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IADIS International Conference WWW/Internet 2010A PERFORMANCE COMPARISON OF DCCP, CTCP, ANDCUBIC, USING VOIP AND CBR TRAFFIC PATTERNSPriscila Doria and Marco Aurélio SpohnFederal University of Campina GrandeAv. Aprígio Veloso, 882, Bodocongó, Campina Grande-PB, BrazilABSTRACTDCCP is a prominent transport protocol that has attracted the attention of the scientific community for its rapid progressand good results. Previous works have compared the performance of DCCP with standard transport protocols, mostlythrough simulation, assuming a single protocol per link and only using the constant bit rate traffic pattern. In this paper,we evaluate the performance of two DCCP variants with highly representative TCP variants: CTCP and CUBIC. The firstone is the TCP variant adopted in the Microsoft Windows Server 2008, and the second one is the TCP variant adopted inthe Linux kernel. In the proposed scenarios, the protocols fight for the same link in contention. Results show that DCCPCCID2 performs better than DCCP CCID3 in scenarios with contention, due to the significantly better fairness of DCCPCCID3. In addition to that, even though CUBIC has been shown to have an aggressive congestion control performingbetter with CBR traffic, results show that CUBIC suffers with the on/off traffic pattern of VoIP applications. Meanwhile,CTCP is outperformed by DCCP and CUBIC in most scenarios.KEYWORDSDCCP, CTCP, CUBIC, Congestion Control, Internet, VoIP.1. INTRODUCTIONMultimedia streaming (e.g., audio streaming, video streaming, VoIP, interactive video) is being consideredan important service in modern networks. This requires that the network protocols used to transmitmultimedia cooperate in harmony with the protocols used for data services. Many real time multimediaapplications prefer UDP as their transport protocol instead of TCP when they need to favor performance overreliability. However, UDP transmissions flow in a fixed rate regardless of the available link bandwidth. Theimpact of the congestion caused by multimedia transmissions that adopt UDP has motivated the InternetEngineering Task Force (IETF) to propose a new Internet standard: the Datagram Congestion ControlProtocol (DCCP). The novelty of DCCP is to prioritize performance, like UDP, but also being able toperform congestion control, like TCP. DCCP is a prominent protocol, gaining the attention of the scientificcommunity, due to its fast development and good results (Kohler et al., 2006).The standard TCP congestion avoidance algorithm employs an additive increase and multiplicativedecrease (AIMD) scheme, which follows a conservative linear growth function for increasing the congestionwindow and multiplicative decrease function in case of packet losses. For a high-speed and long delaynetwork, it takes standard TCP an unreasonably long time to recover the sending rate after a single packetloss event. One straightforward way to overcome this limitation is to modify TCP's increase/decrease rule inits congestion avoidance mechanism, so that the sender increases congestion window more quickly anddecreases it more gently upon a packet loss. This aggressive behavior of such an approach may severelydegrade the performance of regular TCP flows whenever the network path is already highly utilized.However, when an aggressive high-speed variant flow traverses the bottleneck link with other standard TCPflows, it may increase its own share of bandwidth by reducing the throughput of other competing TCP flows.While the delay-based flows respond to increases in RTT, reducing its sending rate, the loss-based flowscontinue to increase their sending rate. Hence, a delay-based flow obtains less bandwidth than its fair share.To circumvent the low utilization problem on high-speed and long delay networks, two novel variants ofTCP were recently proposed: Compound TCP (CTCP) (Tan et al., 2006) and CUBIC (Ha et al., 2005).211